When a nuclear bomb is detonated, intense fluxes of gamma rays, x-rays, and other high energy particles are created. When integrated circuits are exposed to this type of harsh environment, a large number of electrons and holes are generated in the silicon, causing large photocurrents to be generated. Under certain conditions, these photocurrents can lead to rail-span collapse, and burnout of metal lines, contacts, and vias. This damage to the integrated circuits can ultimately result in system failure.
Some integrated circuits are designed to continue operating during and after a nuclear bomb attack or other dose rate event, such as integrated circuits used in strategic weapons systems. Dose rate hardness is a reliability parameter used for determining the hardness of these integrated circuits. The ability to predict the dose rate hardness of an integrated circuit is important for determining which integrated circuits are suitable for use in systems requiring continued operation during a dose rate event.
Dose rate hardness is typically calculated by hand. This hand calculation typically estimates total steady state photocurrent from Vdd to Vss as (dose rate)×(total collection volume). However, this method does not provide detailed nodal information (i.e., information at the nodes between Vdd and Vss). The nodal information is desirable as it can be used to provide a more complete evaluation of whether a particular device is susceptible to damage during a dose rate event.
External testing of devices to determine dose rate hardness may also be performed. For example, Military Handbook MIL-HDBK-815, Dose-Rate Hardness Assurance Guidelines, dated 7 Nov. 1994, and revised by Notice 1, dated 10 Jan. 2002, describes various hardness testing methods. However, these testing methods may be expensive and result in waste (i.e., damaged devices).
Therefore, it would be beneficial to simulate a circuit design exposed to a dose rate event to determine if the circuit meets the dose rate hardness requirements of a particular system.